1. Technical Field
The present disclosure relates to a fabrication processing system of a copper indium gallium selenide (CuIn1-xGaxSe2 or CIGS) thin film solar cell, more particularly to a fabrication processing system CIGS of thin film solar cell equipped with real-time analysis facilities for profiling the elemental components of CIGS thin film using laser-induced breakdown spectroscopy.
2. Description of the Related Art
Plasma generated at the time of laser irradiation emits light of a specific wavelength, so that an elemental components of a materials may be qualitatively and quantitatively analyzed using the collected light.
A laser-induced breakdown spectroscopy (hereafter referring to as LIBS), which is one method for analyzing a elemental component of the material using the collected light, is a spectral analysis techniques using plasma as an excitation source produced by generating a breakdown known as a discharge phenomenon.
A sample within the laser-induced plasma is vaporized such that atoms and ions may be present at exciting state.
The atoms and ions release energy after a certain lifetime and return back to a ground state to emit the specific wavelength based on a type of an element and the exited states. Therefore, by analyzing a spectrum of the emitted wavelength, the elemental components may be qualitatively and quantitatively analyzed.
FIG. 1 illustrates an operating principle of LIBS according to the prior art.
Referring to FIG. 1, first, as described in step 1, when a pulse laser is radiated to ablate a microscopic material (several μg) (The ablation refer to a phenomenon that a material is melted and vaporized by the laser to be removed), the ablated material absorbs laser energy, so that an ionization occurs during very short time and then forms high temperature plasma of about 15000K as described in step 2.
Upon termination of the laser pulse, the specific spectrum corresponding to each element within the plasma is generated while cooling the high temperature plasma. The spectrum generated at this time is collected and analyzed using a spectroscopy device to obtain a specific spectral data, so that the elemental element composition and the amount of the substance included within the material through a data analysis can be measured.
LIBS technique is different from other measurement technique in that:                1) the entire measuring time is within one second,        2) a separate sampling and pretreatment process for measurement is not required,        3) an element configuration of the material can be measured at an accuracy of mm unit while ablating the material in a depth direction due to requiring microscopic amount at one time measurement,        4) a measuring environment is not required and a measurement in air is possible, all elements is analyzed at ppm accuracy except inert gas, and        5) a facility is configured at a relatively low cost.        
FIG. 2 is a chart comparing the different measurement.
Referring to FIG. 2, SIMS (Secondary Ion Mass Spectrometry), AES (Atomic Emission Spectroscopy), EDS (Energy Dispersive X-ray Spectroscopy), GD-MS (Glow Discharge Mass Spectrometry), which is commonly used in the measurement of the distribution of a material make measurement possible only in laboratory level due to the need of high vacuum, but they is not applicable to a line in reality.
In a widely used ICP-MS (Inductively Coupled Plasma-Mass Spectrometry, it is difficult that a sample piece to be analyze should be analyzed after is melted in a solvent, so that it is also impossible to apply to the fabrication line.
XRF (X-ray Fluorescence), which is widely used to a material analysis of the solar cell at a lab or on-site because of simplicity of use has a advantage that makes the measurement in air possible at low-cost, but, it is limited to the measurement for a material distribution of CIGS in that:                1) since the measurement for an lighter elements such as Na, O, N, C, B, Be, Li and the like is nearly possible, Na content measurement within CIGS thin film which has decisive effect on a element efficiency is impossible,        2) since a accuracy of a depth direction for XRF is merely up to about 1 μm, it is impossible that the measurement for the element distribution is implemented in a CIGS thin film of 2 μm in thick at depth direction, and        3) it is difficult to distinguish fluorescence signal whether a fluorescence signal output from the thin film or a from substrate. The prior art has a problem that the material distribution of the thin film is measured.        
Generally, a semiconductor solar cell may be defined as element for converting sunlight directly into electricity using a photovoltaic effect generating electrons by radiating the light to the semiconductor having p-n junction.
A three parts, which is the most basic components, a front electrode, a rear electrode and a light absorbance layer disposed therebetween is formed.
The most important material is the light absorbance layer for determining the photoelectric conversion efficiency and the solar cell may be classified into several types.
This light absorbance layer material refers to CIGS thin film solar cell including Cu(In,Ga)Se2 of I-III-VI2 compound. The CIGS thin film solar cell, which is the solar cell having high efficiency and low-cost type is most obviously noticed as second-generation cells to replace crystalline silicon cells and shows the efficiency closest to monocrtystalline device.
FIG. 3 illustrates schematically a structure of the thin solar cells.
FIG. 4 is a schematic flow chart showing a production process of the thin film module.
A CIGS thin film solar cell is manufactured by sequentially depositing MO layer, CIGS layer, CdS layer and TCO layer, which will be described in more detail as follows.
First, CIGS thin film module is manufactured by depositing Mo, which is a rear electrode layer on a substrate, sequentially depositing CIGS layer and CdS buffer layer, which is a light absorbance layer, on Mo layer, forming a pattern through a scribing process (P1 scribing), sequentially depositing TCO (transparent conductive oxide) layer and a front electrode grid of Ni/Al on CdS layer and finally performing the scribing process (P3 scribing).
The scribing process is a pattering process to be a serial connection in predetermined interval to prevent a reducing efficiency caused by a sheet resistance as a area resistance increases wherein the scribing process consists of a total of three times of P1, P2 and P3. Conventionally, P1 scribing is patterned by a laser and P2 and P3 scribing is patterned by a mechanical method, whereas recently the technique pattering all the P1, P2 and P3 using a laser has been developed.
In such a CIGS thin film solar cell, it is reported that a thickness of the thin film (1˜2.2 μm), an elements structure, a composition of the material consisting of CIGS thin film, which is a pluralistic compound, and an element distribution within the thin film have an decisive effect on a light absorbance rate and a photoelectric conversion efficiency.
It is reported that sodium diffused on CIGS light absorbance layer from soda-lime grass is available generally as a substrate increases a charge density (Nakada et al., Jpn. J. Appl. Phys., 36, 732 (1997)) and increase CIGS single crystal grain size to reduce a properties change, thereby improving the photoelectric conversion efficiency (Rockett et al., Thin Solid Films 361-362 (2000), 330; Probst et al., Proc. of the First World Conf. on Photovoltaic Energy, Conversion (IEEE, New York, 1994), p. 144).
The reports suggest that chemical properties of the light absorbance layer should be controlled through the material distribution within the thin film to provide quality control in the production line of the CIGS thin film solar cell.
Meanwhile, a continuous production process of the CIGS thin film solar cells is classified into a roll-to plate (hereafter, referred to as R2P) process for utilizing a hardened material substrate such as soda-lime and a roll-to roll (hereafter, referred to as R2R) process for utilizing a metal sheet such as stainless steel, Ti, Mo, Cu and the like and a flexible material substrate of polymer and the like such as polyimide.
Since such a continuous production process is not provide with a system for measuring at real time physical and chemical properties of the CIGS thin film affecting on performance of the product on filling date, the inventor cannot help depending on the predetermined value for the physical and chemical properties described above.
In addition, a separate check are impossible even if the physical and chemical stands aiming at a actual production process is deviated and should be found through degradation of performance and quality to generate the loss of a significant product.
A considerable times and effort is taken to check the performance and quality of the products to check physical and chemical variables causing product performance and quality degradation to increase a price, thereby causing competitive degradation. It is preferable that a process control system that measures physical and chemical properties of CIGS thin film without pre-treatment in a real time is provided.